1. Field of the Invention
The present invention generally relates to machine tools and, more particularly, to a machine tool adapted to be controlled by an electric circuit.
2. Description of the Prior Art
Of the boring machines for making one or more holes in a workpiece, a drilling machine, specifically a jig-boring machine, is widely used which employs a drilling tool for making one or more holes in the workpiece. While the present invention is applicable to any type of machine tools designed to bore the workpiece, reference will be made to the jig-boring machine for the discussion of the prior art.
FIG. 6 of the accompanying drawings illustrates an example of the prior art jig-boring machine in schematic side view. As shown therein, the prior art jig-boring machine comprises a drive motor mounted on an upright column 9 and having a drive pulley 2 mounted on a drive shaft of the motor 1 for rotation together therewith. The jig-boring machine 1 also comprises a spindle 4 supported for rotation about its own longitudinal axis by a support sleeve fast with the column 9 and has a driven pulley 3, a drive belt 5 drivingly trained between the drive and driven pulleys 2 and 3 so that the drive of the drive motor 1 can be transmitted to the spindle 4 through the drive belt 5. As shown, each of the drive and driven pulleys 2 and 3 is of a type having belt grooves of different outer diameters, that is, having a large-diameter belt groove, a small-diameter belt groove and an intermediate diameter groove having a groove size intermediate between the large- and small-diameter belt grooves.
The spindle 4 has a lower free end to which a drill chuck 6 is secured for rotation together with the spindle 4, said drill chuck 6 being adapted to receive and support a drilling tool 7 in a removable fashion and positioned immediately above a worktable 8 supported on the column 9 for movement up and down. The sleeve 4 and, hence, the drilling tool 7 received by the drill chuck 6 can be moved up and down in a direction lengthwise of the spindle 4 by turning a manual handle bar 10 drivingly coupled with the sleeve 4 so as to move the latter up and down.
With the jig-boring machine of the above described construction, the boring process is performed in the following sequence.
In the first place, the position of the worktable 8 relative to the upright column 9 has to be adjusted, followed by the placement of a workpiece on the worktable 8 immediately below the drill chuck 6. Thereafter, the drilling tool 7 of a design appropriate to the size of a hole desired to be formed in the workpiece is secured to the drill chuck 6. After the seed of revolution of the spindle 4 has been selected in consideration of the material of the workpiece and the size (diameter) of the drilling tool 7, the drive belt 5 trained between the drive and driven pulleys 2 and 3 is repositioned so as to engage in one of the belt grooves of different diameters in each of the drive and driven pulleys 2 and 3 so that the seed of revolution of the spindle 4 can attain a desired or required value selected in the manner as hereinabove described. The drive motor 1 is then electrically energized to drive the drive pulley 2 and, hence, the sleeve 4 through the drive belt 5. While the sleeve 4 is so driven about its own longitudinal axis, the manual handle bar 10 is turned so as to lower the spindle 4 with the drilling tool 7 subsequently driven into the workpiece on the worktable 8 to form a hole.
When it comes to the replacement of the drilling tool 7 with a different drilling tool, the drill chuck 6 has to be loosened or undone to allow the drilling tool 7 to be released therefrom, followed by the insertion of the different drilling tool into the same drill chuck 6 with the drill chuck 6 subsequently fastened to firmly hold the different drilling jig.
According to the prior art jig-boring machine of the type described above, unless the replacement of the drilling tool is carried out by a skilled attendant worker, it often occurs that the drilling tool may be inserted into the drill chuck in the wrong way, for example, slantwise relative to the drill chuck or in axially offset relationship with the center of the drill chuck. The worst of all is that the drilling tool may be bent or broken and that a hole subsequently formed in the workpiece may depart from the design requirements. In view of the foregoing, the prior art drilling machine requires a skilled attendant worker to perform the replacement of the drilling tool.
While the types of drilling tools available for one particular type of machine tool are many, and while automated drilling machines are also currently available and utilized, an automatic replacement of the drilling tools in the automated drilling machines has not yet been accomplished because the mounting of any one of the drilling tools on the drill chuck cannot be performed without difficulty.